import java.util.Scanner;

public class 圆面积 {
    public static void main(String[] args) {
        getCircularArea();
    }

    public static void getCircularArea() {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入圆的半径：");
        double r = sc.nextDouble();
        System.out.println("圆的面积为：" + Math.PI * Math.pow(r, 2));
    }
}